Gaseous discharge device



Feb. 5, 1952 P. w. STUTSMAN GASEOUS DISCHARGE DEVICE 2 SHEETS-SHEET 1 Filed June 25, 1949 EW Q p.

.006MFD 50 K SIGNAL INPUT Wvsmm PA UL W STUTSMAN ATTQRNEV 1952 P. w. STUTSMAN GASEOUS DISCHARGE DEVICE 2 SHEETS-SHEET 2 Filed June 25, 1949 lNVE/WUR PAUL. W. STUTSMAN BY w ATTORNEY Patente Feb. 5, 1952 GASEOUS DISCHARGE DEVICE Paul W. Stutsman, Needham, Mass., assignor to Raytheon Manufacturing Company, Newton, Mass., a corporation of Delaware Application June 25, 1949, Serial No. 101,285

3 Claims. 1

This application relates to electron discharge devices and more particularly to gas-filled dis charge devices of small size.

Heretofore, it has been difficult to manufacture gas discharge devices of a small size which would carry heavy currents and operate for a long period of time without failure. This is due in part to a tearing off of particles of molecula size from the electron emissive coating of the cathode by high peak currents. The particles then occlude the gaseous filling of the tube and may be deposited on other elements of the device, thus depleting the store of electron emissive material on the cathode until ultimate failure of the device occurs. The occlusion of the gaseous medium by the electron emissive material detracts from the gaseous pressure, thus varying the operating characteristics of the tube and more particularly increasing the rate at which cathode deterioration takes place, since cathode deterioration in general varies inversely as a function of the pressure of the gas in the tube. This phenomenon is particularly true of gas discharge devices employing a cold cathode.

A further difilculty, encountered in producing gas discharge tubes of subminiature size, occurs from breakdown between the elements of the tube, for example, between the anode and cath-. ode at relatively low voltages. It has been found that this difficulty can be overcome by placing adequate shielding grids between the anode and cathode.

Further, in cold cathode tubes it has heretofore been difllcult, if not impossible, to fire the tube by the application of a suitable low potential to a control grid. This difiiculty has been overcome by maintaining a keep-alive current between the cathode and a keep-alive electrode positioned ad-,

jacent th cathode. By positioning the keepalive electrode at the minimum breakdown distance from the cathode, a keep-alive ionic discharge may be initiated with the lowest possible voltage applied between the keep-alive electrode and the cathode. If the spacing between the keep-alive electrode and the cathode is either increased or decreased, the necessary breakdown voltage which must be applied will be increased. For example, in the present tube having a spacing of approximately twenty thousandths of an inch between keep-alive electrode and the cathode and a particular gas filling described hereinafter, such that the voltage required to produce a glow discharge between the cathode and the keep-alive electrode is on the order of 60 volts, the initial voltage required to break down the space 2 between the keep-alive electrode and the cathode into an ionic discharge will be, with good electrode design, in the range of -90 volts.

The close positioning of the keep-alive electrode to the cathode in this tube structure has been found to decrease the drop between the keep-alive electrode and the cathode to a point where it is approximately equal to the cathode fall. The positive column drop of the gaseous medium has been substantially eliminated with the result that there is a lower overall voltage drop between the cathode and keep-alive electrode and hence a minimum power required to maintain a keep-alive discharge. In this particular tube the keep-alive current may be with in the range of 10-30 milliamperes. Since the positive column drop in the gaseous medium itself hasbeen reduced to substantially zero, oscillations both of the high-frequency type due to electron interaction and of the lower audio-frethrough the grid structure and accelerated to ward the anode.

These electrons will attain a suificient velocity due to the anode-to-grid potential to ionize the gaseous medium between the anode and grid thereby establishing conduction to the cathode and firing the tube.

As a result, it may be seen-that applicant has produced a discharge device having relatively low stand-by power consumption, a large current discharge capacity, a low starting voltage and tube drop and a long cathode life, all these features being incorporated in a subminiature tube.

Further, applicant discloses herein, by way of example, circuits particularly adapted to utilize the discharge devices herein described.

The particular details of illustrative modifications of this invention whereby the foregoing results are obtained will now be described in detail, reference being had to the accompanying drawings wherein:

Fig. 1 represents one embodiment of the invention showing a cross-sectional view thereof taken along line ll of Fig. 2;

Fig. 2 illustrates a cross-sectional view of the device illustrated in Fig. 1 of Fig. 1;

Fig. 3 illustrates a circuit utilizing the discharge device, shown in Figs. 1 and 2;

Fig. 4 represents a cross-sectional view of a second species of the invention taken along line 4-4 of Fig. 5; Fig. 5 represents a cross-sectional view of my invention taken along line 5-5 of Fig. 4; and

Fig. 6 represents a circuit diagram illustrating one use oi the species, shown in Figs. 4 and 5.

Referring now to Fig. 1, there is shown a glass envelope 29 consisting of a tube, one end of which is pressed together as at 2| and through which extend a plurality of lead-in wires. The other end of the glass tube 29 is curved together and contains at its center a 'mass of glass 22 which is used to seal the envelope after filling oi the envelope with the correct gaseous medium. Extending upward from the glass press 2| inside taken along line 2--2 envelope 29 are three glass tubes 23, 24 and 25 whose axes are all parallel and lying in the same plane and spaced an equal distance apart. The center glass tube 24 extends slightly .less than half the length of envelope 29. Inside the glass tube 24, which is hollow, is an anode rod 26 which extends from the open end of the glass rod 24 toward the glass press 2| through a spacer 21 consisting of a wire spirally wrapped around anode rod 26. Anode rod 26 is then joined, for example,

. by welding to a lead-in wire 29 which extends through the glass press 2|.

The end of the tube 24, which is open, is covered by a cup-shaped grid 29 of wire mesh which may be made of 60 x 60 strands per inch screening using .005 inch nickel wire. The diameter of aiseqrss 33. The mica plate 33 is flat and has a shape con- 7 forming to the inside contour of the envelope 26 at a section taken at right angles to the rods 36. Tabs 36a are welded to rods 35 on both sides 0! plate 33, thereby preventing movement of plate 33 on rods 35. f

A cathode 39 is supported between the rods 35 in the space between the mica plate 33 and the bottom of the cup-shaped grid 32. This cathode consists or a helically-wound wire coated with electron emissive material, the diameter of said helix being approximately equal to the diameter oi! the glass tube 24. One end of said helically-wound wire is attached as by welding to one of the rods 35 and the other end tothe other rod 35. I

Between the cathode 39 and the cup-shaped grid 32 there is positioned a keep-alive grid 49. This grid is a semicylindrical piece of screening of the same type used to make grids 29 and 32. The axis of the semicylindrical screen is approximately concentric with the axis oi! the helical cathode'39. The: diameter of the cylindrical screen 49 is slightly greater than the helix of the cathode 39 such that grid 49 is in close proximity with the cathode 39. The grid 49 is supported at each end by straps 4| welded thereto and which are attached to bands 42 mounted the cup-shaped grid 29 is slightly larger than the diameter of the glass tube 24 and extends for somewhat more than one diameter of the glass tube over the end of said rod. The bottom oi. said cup-shaped grid 29 is in close proximity but not touching the end of the tube 24 and the anode element 26. Cup-shaped grid 29 is supported by being attached as by welding to a strap 39 at the lip of said cup-shaped grid. The strap 39 extends around the tubes 23 and 25 thereby rigidly supporting the grid 29. The tubes 23 and 25 are somewhat longer than the tube 24 and extend further into the envelope 29 past the end of tube 24 and the grid 29. A lead-in wire 3| is attached to the strap 39 as by welding and extends along the side of envelope 29 through the glass press 2|.

Surrounding the grid 29 is a second cup-shaped grid 32 which is similar in shape to grid 29 but somewhat larger in diameter. The second grid 32 is supported by a strap 33 placed around the rods 23 and 25 similar to the support of grid 29, and a lead-in member 34 attached to strap 33 extends through the glass press 2|. The bottoms of grids 32 and 29 are spaced somewhat from each other and the straps 33 and 39 are spaced from each other along the rods 23 and 25 with the result that the grid 32 is insulated from the 7 grid 29. The glass rods 23 and 25 extend slightly beyond the bottom of cup-shaped grid 32.

Extending the length of rods 23 and 25, which are hollow, are a pair of support rods 35 which are butt-welded to lead-in members 36 extending through the glass press 2 l. The rods 35 contain spacers 31 thereon similar to the spacer 21 on anode rod 26. The rods 35 extend out of the open ends oi! the glass rods 23 and 25 for a distance equal to approximately half the diameter of envelope 29 and then pass through a mica plate on the tubes 23 and 25. The grid 49 is connected of envelope 29 through the glass press 2|. Leadin wire 43 also extends in the other direction through the mica plate 33 and is welded to a strap 44 containing getter material placed in two detents therein. v

It may be seen that, by using grids which are cup-shaped,'the anode is adequately shielded from other elements of the tube thereby preventing fiashover at low anode to cathode yoltages.

Referring now to Fig. 3, there is shown a circuit to be controlled by this discharge tube comprising a relay coil 45 attached to the anode 26 of the tube and to ground through a condenser 46, for example, or 10 microfarads. A junction between coil 45 and the condenser 4'6 is connected to 3+ through a resistor 41 which may be, for example, 7 kilohms. Grid 29 adjacent anode 26 is connected to 13-!- through a resistor 43 01', for example, 2490 ohms. Grid 32 is connected to ground through a 1 megohm grid-leak resistor 49 and to a source oi. signals through a D. C. blocking-condenser 59 which may be, for example, .096 microfarad. The keep-alive grid 49 adjacent the cathode 39 is connected to 3+ through a resistor 5| of, for example, 5 kilohms. The cathode 39 is connected to ground.

Due to the potential between keep-alive grid 49 and the cathode 39, an ionic discharge occurs therebetween causing current to flow through resistor 5| and the voltage of the keep-alive grid 49 to drop from the value of 3+ which'may be, for example, volts to a lower voltage of, for example, 10 volts. This ionic discharge produces a source of electrons in the vicinity of the cathode.

With no signal on grid 32, said grid being tied to the cathode potential through resistor 43, no current will flow to the anode 25 since the anode 26 is efiectively shielded from the cathode by the grid 32. However, ii. the grid 32 is driven positive by a signal, electrons will be attracted from the arc discharge existing between the keep-alive grid 49 and the cathode 49 and will pass through the space of grid 32 and the grid 29 striking the anode 26. As the electrons pass from the cathode 29 to the anode 26, they strike molecules of the gaseous medium contained therein causing ionization of the molecules. The positive ions thus created are attracted to the cathode 39, due to its negaerates the relay to perform its function. The

surge of current discharges the condenser 46 and causes the anode potential 26 to drop to a low value thereby extinguishing the discharge between the anode and cathode. The condenser then recharges through resistor 41 in preparation of the next discharge of the tube 20. By the use of the keep-alive grid 40 it is possible to eliminate a cathode heater and further to more easily control the discharge. The input signal to grid 32 required to fire the tube may be, for example, on the order of volts at a currentof 100 microamperes.

The gas used for this tube may be xenon at 20-40 millimeters pressure. Since xenon molecules have a low thermal conductivity, they act as a good heat insulator thus preserving the cathode heat. Furthermore, since the molecules have a large mass, they efiiciently transfer energy from their momentum into heat upon striking the cathode. Due to the highe pressure, deterioration of the cathode is minimized, and due to the efiicient heating, less power is required at the signal input grid to transfer the discharge from an ionic discharge between the cathode and the keep-alive grid to an arc discharge between the cathode and anode. By the use of the glass tubes 23 and 25, the leads 36 at cathode potential are shielded, as they pass near the anode and grid elements, thus further helping to prevent low anode to cathode discharges.

Referring now to Figs. '4 and 5, there is shown a modification of the species illustrated in Figs. 1 and 2, like parts of the different species being referred to by the same reference numerals. The species of Figs. 4 and 5 difier from the species of Figs. 1 and 2 in that the grid 32 and its supporting strap and lead-in member have been eliminated.

Referring to Fig. 6, there is shown the diagram of a circuit utilizing this modification. The anode and keep-alive grid circuits are simlar to Fig. 3. The signal input is now applied to the grid 29 through a 100 kilohm grid current limiting resistor 51 and the D. C. blocking condenser 50. The grid 29 is returned to ground by having the junction between the grid current limiting resistor 5| and the input D. C. blocking condenser 50 returned to ground through a grid load resistor 49 and a source of bias voltage 52. This bias voltage is necessary since in the absence of the secand shield 32 a zero bias on grid 29 allows the tube to fire. Thus it may be seen that while the species of Figs. 4 and 5 eliminates one grid, it requires a bias source not required by the species of Figs. 1 and 2.

Since, in both Figs. 1 and 4, the cathode comprising the helical coil 39 is led out through two leads 36, an external voltage may be applied between leads 36 causing a current to flow through cathode coil 39 to heat the same. As a result, the cathode will operate as a directly heated thermionic emitter and if desired, the keep-alive current and electrode may be eliminated for this type of operation.

This completes the description of the details of the specific modifications of the invention illustrated herein. However, many variations thereof will be apparent to persons skilled in the art without departing from the spirit and scope of this invention. For example, additional grids of the types 29 and 32 could be added and the particular methods of support and connection of the various electrodes could be modified. Therefore, applicant does not Wish to be limited to the specific details of the invention described herein except as defined by the appended claims.

What is claimed is:

1. An electron discharge device comprising an envelope containing a cathode, an anode surrounded by a sleeve of insulating material, a plurality of grids surrounding said insulating sleeve and said anode, and a keep-alive electrode positioned at substantially the minimum breakdown distance from said cathode.

2. An electron discharge device comprising an envelope containing an ionically heated cathode,

an anode surrounded by a sleeve of insulating material, and a plurality of grids surrounding said insulating sleeve and said anode.

3. An electron discharge device comprising an envelope containing a cathode, an anode surrounded by a sleeve of insulating material, a cupshaped grid surrounding said insulating sleeve and said anode, and a keep-alive electrode positioned at substantially the minimum breakdown distance from said cathode.

PAUL W. STUTSMAN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,784,869 Gray Dec. 16, 1930 1,987,645 Steenback Jan. 15, 1935 2,062,268 Knowles Nov. 24, 1936 2,090,951 Schlesinger Aug. 24, 1937 2,139,898 Kock Dec. 13, 1938 2,203,452 Berghaus June 4, 1940 2,295,569 Depp Sept. 15, 1942 2,433,813 Hilliard Dec. 30. 1947 

